PROJECT SUMMARY Obesity is prevalent in one third of American adults and children and costs the American health care system billions of dollars yearly. There are strong associations of low vitamin D levels with obesity, yet an underlying causal relationship has not been identified. Multiple clinical trials have been performed to use vitamin D as a treatment for obesity with conflicting results. The extensive impact of obesity on patients and its cost to society make the establishment of effective treatments urgently necessary. However, treating obesity and decreasing its prevalence cannot occur until we understand the mechanisms underlying the onset and progression of obesity. One of the possible mechanisms linking obesity and low vitamin D levels is through the brain. Accumulating evidence indicates that the brain has receptors for vitamin D in key weight regulatory regions and that vitamin D has impaired transport across the blood-brain-barrier. However, the potential CNS regulation of weight by the vitamin D receptor has not been studied. Dr. Sisley's long-term research objective is to unravel the vitamin D-dependent mechanisms underpinning childhood obesity and to translate these findings into new therapeutic options for the pediatric population. In this proposal, Dr. Sisley will focus on the mechanisms by which vitamin D may act in the brain to regulate weight. Her preliminary data have revealed the ability of the active ligand for the vitamin D receptor, 1,25-dihydroxyvitamin D3 (calcitriol; 1,25D3) to dramatically reduce food intake, body weight, and specifically fat mass in obese rodents when delivered directly into the brain. Additionally, she demonstrates 1,25D3 has direct actions to depolarize POMC neurons, which are known to decrease food intake. Last, her data show a physiological role for the vitamin D receptor in the brain. The following specific aims will use advanced in vivo and molecular techniques to determine the mechanisms underlying vitamin-D mediated weight loss. In Aim 1, she will determine if the VDR in POMC neurons is required for normal weight regulation using a Cre-lox approach. In Aim 2, she will test the hypothesis that 1,25D3 signals through the VDR in POMC neurons to cause anorexia through in vivo food intake experiments, ChIP assessment of VDR binding to the POMC promoter, and genomic/transcriptomic experiments. Aim 3 will investigate the requirement of melanocortin-4 receptors, a downstream target of POMC, in the anorectic effect of 1,25D3. The primary goal of this mentored career development award is to advance Dr. Sisley forward in her pursuit of an independent research career. Dr. Sisley has a strong publication and grant record from her fellowship and has excellent techniques in the physiological in vivo metabolic testing of rodents. Her career development plan includes informal and formal training in nuclear receptor biology and genomic level investigational techniques. Additionally, she will gain training in mouse genetics, neuroanatomy/physiology, and vitamin D signaling. She will use a combination of focused-symposia, national meetings, didactic courses, and individualized mentorship to achieve her training objectives. Her current appointment at the Baylor College of Medicine gives her a strong research environment with both experts in nuclear receptors, core facilities in genomic techniques, and significant institutional support (as evidenced by her start-up funds and Letter of Institutional Support). She has strong mentorship under Dr. David Moore, an expert in nuclear receptors, as well as new mentorship under Dr. Nancy Weigel (vitamin D) and through UT Southwestern, Dr. Joel Elmquist (hypothalamic weight regulation). Additionally, she has contributors to aid her progress in every aspect of her training. This combination of a strong PI, excellent mentorship, and focused training goals at a renowned research institution poises Dr. Sisley for ultimate success as an independent investigator.